<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>


    <title>Help - Multi-Temporal Speckle Filter</title>
    <link rel="stylesheet" href="../style.css">
</head>
<body>

<table class="header">

    <tbody>
    <tr class="header">

        <td class="header">&nbsp;Speckle Filter</td>


        <td class="header" align="right"><a href="../general/Overview.html"><img src="../images/snap_header.jpg"
                                                                                 border="0"></a></td>

    </tr>

    </tbody>
</table>


<h3>Multi-Temporal Speckle Filter Operator</h3>

<p>
    SAR images have inherent salt and pepper like texturing called speckles which
    degrade the quality of the image and make interpretation of features more
    difficult. The speckles are caused by random constructive and destructive interference
    of the de-phased but coherent return waves scattered by the elementary scatters
    within each resolution cell. Multi-temporal filtering is one of the commonly used
    speckle noise reduction techniques.
</p>

<h4>Multi-Temporal Speckle Filtering</h4>

<p>
    For a sequence of <span style="font-style: italic;">N</span> registered multitemporal images, with intensity at
    position
    (<span style="font-style: italic;">x, y</span>) in the <span style="font-style: italic;">k</span>th image denoted by
    <span style="font-style: italic;">I</span><sub style="font-style: italic;">k</sub><span style="font-style: italic;">(x, y)</span>,
    the temporal filtered images are
    given by:
</p>
<br>

<div style="margin-left: 40px;"><img style="width: 255px; height: 58px;" alt=""
                                     src="images/multi_temporal_filter_eq_1.jpg"><br></div>
<br>&nbsp;&nbsp;&nbsp;for <span style="font-style: italic;">k</span> = 1, ..., <span
        style="font-style: italic;">N</span>, where <span style="font-style: italic;">E</span>[<span
        style="font-style: italic;">I</span>] is the local mean value of pixels in a window centered at (<span
        style="font-style: italic;">x, y</span>) in image <span style="font-style: italic;">I</span>.

<br><h4>Pre-Processing Steps</h4>&nbsp;&nbsp;&nbsp;The operator has the following two pre-processing steps:<br>
<ol>
    <li>The first step is calibration in which &#963;<sup><sub>0</sub></sup>
        is derived from the digital number at each pixel. This ensures that
        values of from different times and in different parts of the image are
        comparable.
    </li>
    <li>The second step is registration of the multitemporal images.</li>
</ol>
&nbsp;&nbsp;&nbsp;Here it is assumed that pre-processing has been performed before applying
this operator. The input to the operator is assumed to be a product
with multiple calibrated and co-registered bands.
<br><h4>Parameters Used</h4>
&nbsp;&nbsp;&nbsp;The following parameters are used by the operator:
<ol>
    <li>Source Band: All bands (real or virtual) of the source product. User can
        select one or more bands for producing the filtered image. If no bands are
        selected, then by default all bands will be selected.
    </li>
    <li>Window
        Size: Dimension of the sliding window that is used in computing spatial
        average in each image of the temporal sequence. The supported window sizes are
        3x3, 5x5, 7x7, 9x9 and 11x11.
    </li>
</ol>
<img style="width: 500px; height: 500px;" alt="" src="images/multi_temporal_filter_dlg.jpg">
<br>
<br>
<br>
Reference: S. Quegan, T. L. Toan, J. J. Yu, F. Ribbes and N. Floury, &#8220;Multitemporal
ERS SAR Analysis Applied to Forest Mapping&#8221;, IEEE Transactions on
Geoscience and Remote Sensing, vol. 38, no. 2, March 2000.

<hr>
</body>
</html>